1. Field of the Invention
The present disclosure pertains to the use of biopolymer substrates in the remediation of contaminated materials. More particularly, the disclosure relates to the use of certain bioremediation enhancing agents that facilitate the chemical, physical and biological transformation of certain metals and minerals associated with Mine Influenced Water (MIW). MIW is water that can contain metals or minerals associated with the disturbance of soil and/or rock that has been exposed to air and/or water and includes water commonly referred to as Acid Mine Drainage.
2. Description of Related Art
The use of carbon substrates to promote reducing conditions within a subsurface to remediate contaminants has been a commercial option since the early 1990's and in some cases even before 1990. Bacteria and other microbes metabolize the carbon substrate as an electron donor along with an electron acceptor thereby obtaining energy for growth and reproduction. Under certain pH and reductive-oxidation potentials (a measure of a substance's affinity for electrons and commonly referred to as oxidation/reduction potential, ORP, or reductive-oxidation potential, redox), many dissolved metals and minerals may be used as electron acceptors and can be chemically changed through metabolic and chemical processes.
Typical MIW exhibits low pH due to high levels of sulfate either chemically or biologically leached from exposed minerals such as pyrite. Other types of MIW exhibit high pH and high levels of dissolved metals. Lower pH water further promotes the dissolution of metals associated with the parent material. The use of carbon substrates to promote biological treatment of MIW is limited by an inefficiency of microbial populations to precipitate a large amount of metals within contaminated water and the microbial populations' inability to establish and maintain pH to prevent resolublization of the metals. Chemical neutralization of acidic solutions is a basic chemical reaction that is a well known process and is routinely used in water treatment solutions and acid mine drainage treatment systems. However, chemical neutralization is inefficient in removing metals over an extended period of time due to a need to continuously add chemicals to balance the pH.
Chitosan is a deacetylated derivative of chitin that that exhibits chelating properties. Differing degrees of chitin deacetylation exhibit different chelating capacity. The greater amount of deacetylation, the greater the chelating properties.
U.S. Pat. No. 7,138,059 issued to Sorenson et al. (Nov. 21, 2006) discloses addition of organic carbon, such as chitin complex for bioremediation. The full content of the '059 patent is hereby incorporated into this disclosure by reference. Although the '059 patent discloses using chitin as an electron donor to facilitate bioremediation of environmental contaminants, it does not contemplate adding the chitin in an amount sufficient to increase the pH of an acidic contaminated medium to an extent that would increase metal precipitation from the contaminated medium. The systems disclosed in the '059 patent are also limited by their inability to increase or maintain initial pH conditions to support the growth of sulfate reducing microbes for a sufficient period of time to allow for the establishment of facultative microbial populations capable of biologically isolating the sources of metals and minerals associated with MIW.